I haven’t had the talk yet with my kids: my 11-year-old son and 6-year-old daughter. I mean the one about global warming, about what’s coming. But then, we grown-ups haven’t had the talk yet among ourselves. Not really. We don’t seem to know how: the topic is apparently too big and scary. Or perhaps, for the uninformed (or misinformed), not scary enough.

We might take a cue from Mark Hertsgaard’s “Hot,” which raises the emotional stakes while keeping a clear head. This was the first book on climate change that not only frightened me — plenty have done that — but also broke my heart. It happened first on the dedication page, where he writes, “For my daughter, Chiara, who has to live through this.” And again, as I read his epilogue: a letter addressed to Chiara on her 15th birthday, in 2020 — a “cardinal date,” Hertsgaard rightly calls it. “According to the scientists I interviewed,” he tells her, “many, many things have to happen by 2020 if this planet is to remain a livable place.” That is, if the storms, droughts, rising sea levels and mass extinctions of species are to remain within “manageable” limits.

Hertsgaard, to his credit, refuses to sugarcoat these facts. For all the justifiable fears about flooded coastlines, he writes, the “overriding danger” in the coming years is drought. “Floods kill thousands, drought can kill millions,” one expert told him. Within two decades, the number of people in “water-stressed countries” will rise to three billion from 800 million.

And yet Hertsgaard also knows that we cannot allow fear or despair, or even anger, to be our only response. To face this challenge, we need reasons to believe the task is doable. Hertsgaard makes a valiant effort to provide them. He presents a strong case that there is still time to make an enormous difference. We know what to do, and much of the technology already exists. But we must act now.

Hertsgaard, a veteran journalist, had his awakening in October 2005. Interviewing David King, at the time Britain’s chief climate scientist, he realized that human-caused climate change is not a distant threat but already upon us. “Scientists had actually underestimated the danger,” he writes. “Climate change had arrived a century sooner than expected.” What’s more, given our current trajectory — economic, cultural and, most important, political — it’s guaranteed to get a lot worse before it gets any better. (Significant impacts like sea-level rise are now “locked in.”) And it won’t get any better — indeed, it will become truly unmanageable — if we don’t make the necessary cuts in global greenhouse emissions.

This leads Hertsgaard to what he calls the new “double imperative” of the climate fight. “We have to live through global warming,” he writes, “even as we halt and reverse it.” In other words, while deep emissions cuts (what experts call “mitigation”) remain the top priority, that alone is no longer enough. We also have to do everything we can to prepare for the effects of climate change.

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Adaptation — strengthening levees and sea defenses, safeguarding water and food supplies, preparing for more intense heat waves — has long been a touchy subject among advocates, who warn that it signals resignation, or a false sense of security (that we can continue adapting indefinitely), and that it steals resources from the all-important focus on mitigation. But the debate is shifting, and climate adaptation is starting to get the attention it deserves.

There’s not much new in what Hertsgaard advocates on the mitigation front — a “Green Apollo” program with an economy-wide price on carbon, vastly increased energy efficiency, huge investments in clean-energy technology, and other mainstream ideas. His significant contribution is his ground-level reporting on adaptation efforts around the world, from American cities to Bangladesh to the Sahel. All the stories are sobering, but many are also surprisingly hopeful: the Netherlands’ bold 200-year plan to save the country from a devastating sea-level rise; the utterly unexpected success of farmers in Mali, Niger and Burkina Faso in reclaiming huge areas of arable land from desertification; China’s research on large-scale ecological agriculture.

But most important, what Hertsgaard finds is that the ability to adapt to climate change depends as much on “social context” — defined as “the mix of public attitudes, cultural habits, political tendencies, economic interests and civic procedures” — as on wealth and technological sophistication. Wealth and technology clearly matter, but politics and culture may trump them. Take Louisiana: efforts to prepare for future hurricanes, Hertsgaard writes, “have been crippled by the state’s history of poor government” along with “its continuing reluctance — even after Katrina — to acknowledge the reality of global warming for fear that might harm oil and gas production, and an abhorrence of taxes and public planning as somehow socialistic.”

In fact, Hertsgaard’s reporting makes me wonder if there isn’t more hope for the Sahel than for the vulnerable South and Southwest of the United States. After all, why prepare for something — much less try to halt it — if you refuse to believe it’s happening?

The American social context too often remains the largest obstacle, Hertsgaard observes, not only to adaptation at home but to cutting emissions globally. It’s not clear how to change this, but an honest, urgent, grown-up national conversation — beginning in Washington — would be a start.

HOT

Living Through the Next Fifty Years on Earth

By Mark Hertsgaard

339 pp. Houghton Mifflin Harcourt. $25.

Wen Stephenson is a former editor of The Boston Globe’s Ideas section.

A version of this review appears in print on February 6, 2011, on Page BR8 of the Sunday Book Review with the headline: Poisoning the Well. Today's Paper|Subscribe